Abstracts

Rationale: Polyhydramnios, megalencephaly, and symptomatic epilepsy syndrome (PMSE) is a severe developmental disorder characterized by intractable epilepsy, craniofacial dysmorphism, cognitive impairment, and a high childhood mortality rate. PMSE results from a loss of the pseudokinase STRADA, which serves as an upstream regulator of mTOR signaling. Dysregulated mTOR signaling has previously been implicated in several autism-spectrum epilepsy disorders, and thus PMSE provides a novel disorder through which to investigate how mTOR hyperactivation contributes to abnormal brain development and epilepsy. Previous work in our lab established that knockdown (KD) of STRADA in the developing mouse brain is associated with aberrant cortical lamination and mTOR hyperactivity. We sought to define mechanistically STRADA s role in neuronal migration. Additionally given that PMSE patients express 100% penetrance of infantile-onset seizures, we chose to investigate the functional link between STRADA depletion and epilepsy.Methods: We have devised a novel wound healing migration assay for mouse neural progenitor cells (mNPCs) in vitro in order to evaluate migratory capacity in STRADA-deplete cells, a subset of which are treated with the mTOR inhibitor rapamycin. In vivo, in utero electroporation is performed in mice at embryonic day 14 (E14) to transfect neural progenitor cells adjacent to the lateral ventricle with a GFP-tagged shRNA plasmid conferring KD of STRADA, with or without rapamycin treatment. Transfected animals are sacrificed at either E14 for analysis of cortical lamination or postnatal day 7 (P7) for calcium imaging analysis of neocortical activity associated with STRADA KD.Results: In vitro, STRADA KD is associated with significantly reduced migration in mNPCs, rescued with rapamycin treatment. Video microscopy reveals that STRADA KD cells show significantly greater variance in their direction of movement than do their control counterparts (See Figure, Scram control versus STRADA KD). In vivo, the lamination defect associated with STRADA KD is rescued by rapamycin treatment, indicating an mTOR dependence of STRADA s role in cortical development. Additionally, calcium imaging reveals that STRADA KD is associated with neocortical hyperactivity in the region of cortex overlying the area of laminar defect.Conclusions: STRADA plays a critical role in the migration of neural progenitor cells and thus importantly in cortical lamination, in an mTOR-dependent manner. Given that mTOR inhibition with rapamycin rescues migratory and laminar defects associated with STRADA loss, our work provides key preclinical data for the role of mTOR inhibition during brain development as a therapy for minimizing the devastating consequences of several autism-spectrum and epilepsy disorders associated with loss of mTOR inhibition. Additionally, we demonstrate for the first time a functional link between STRADA and epilepsy. Taken together, our results characterize the critical importance of the novel protein STRADA in brain development.